A cabbage responds to high temperature by immediately ceasing to grow. Plants below 45 deg. F. (7 deg. C.) hardly grows at all, and below 32 deg. F. (0 deg. C.), they are quite at a standstill. Hot weather above 80 deg. F. (27 deg. C.) kills plants by causing bolting. From 60 deg. F. to 70 deg. F. (15 deg. C. to 21 deg. C.), growth proceeds steadily.
Cold Stress Response
- Photosynthesis slows below 50°F (10°C)
- Enzymes stop functioning at 32°F (0°C)
- Ice crystals rupture cells below 25°F (-4°C)
Heat Stress Reactions
- Respiration exceeds photosynthesis above 80°F (27°C)
- Bolting initiates at 5+ days above 80°F (27°C)
- Leaves wilt and heads soften in sustained heat
Recovery Techniques
- Cold-damaged plants need gradual warming
- Heat-stressed cabbages require deep cooling
- Trim damaged tissue after temperature extremes
Protection from frost can be achieved with row covers when the temperature dips to freezing. For temperatures of 28°F (-2°C) and below, use a heavyweight cover and anchor the edges with soil to prevent damage. In warmer weather, when the temperature exceeds 40°F (4°C), be sure to remove the fabric to prevent plants from overheating or contracting diseases.
When fighting against heat stress, shade cloth (30% shade) should be placed 3' above the crops dipped into during the hottest parts of a summer day. Deep watering occurs in the morning during heatwaves, and then a light mist can be applied at night to help cool the plant.
Monitor the temperature of your soil, not the air. Soil colder than 45°F (7°C) prevents the plant from drawing up a great many of the needed nutrients in a day. Mulch with dark material to warm the soil in spring, with light mulch to cool it in summer. Thermometers inserted at a depth of four inches give the proper readings.
Match the climates to the variety offered. Some types are winter-hardy and will withstand frost, while others are heat-tolerant and don't bolt. Take care to plant at times when heads will form, when temperatures are between 60°F and 70°F (15-21°C) for optimal growth.
Read the full article: 5 Key Signs: When to Harvest Cabbage
